2 stroke thread (with occasional F1 relevance!)

[uniflow]

Nothing comes down faster than a vertical take off machine, upside down!

[manolis]

Hello Henry.

For a flying machine (helicopter, airplane etc) the Power-to-Weight ratio of the engine is significant.

The weight comprises the engine weight and the weight of the required fuel at take off.
A Wankel Rotary engine appears lightweight, but if the fuel weight is taken into account it is not.

For a Portable Flyer the Power-to-Weight ratio of the engine(s) is crucial / vital.

With short stroke (30mm per piston for a “combined” stroke of 60mm, in the first OPRE Tilting prototype) when the engine is running at 12,000rpm the mean piston speed is only 12m/sec, and when the engine is running at 9,000 rpm the mean piston speed is only 9m/sec (i.e. as fast as the mean piston steep – at continues operation - of some giant two-stroke Marine Diesels, those with the Top Thermal Efficiency among all engines).

Rid of reed valves and of rotary valves (weight, size, reliability issues),
with the thrust loads taken at the cold side of the piston skirt, away from the combustion,
with compact combustion chamber and a lot of squeeze,
with additional time for efficient combustion (pulling connecting rod arrangement),
with perfect balancing (true vibration-free operation) allowing the simple mounting on a extremely lightweight frame secured on the shoulders of the rider / pilot (who cannot tolerate vibrations),
without the need of a tuned / heavy exhaust,
it fits better with a true “portable” Flyer.

The gyroscopic rigidity is another "big" issue addressed by the architecture of this Portable Flyer, enabling easy, instant and accurate control over the flight.

The first prototype we made:



has:
333 cc, bore 84mm, stroke 30+30=60mm
(same bore to stroke ratio with BMW's boxer R1200GS of 2013)
weight: 8.5Kp (19lb) without the exhaust pipe and the carburetor
height: 250mm

As a proof-of-concept low-budget prototype it has a lot of unnecessary material (weight) on it.

Each of the two high-revving OPRE-Tilting engines of the Portable Flyer will have (together with its transmission, i.e. the sprockets and the belts, and the rotors/propellers it drives) a weight of about 6Kp.

The two fuel tanks are to be located / secured on the legs, just above the ankles of the pilot / rider.

“And what about when the fuel tanks are almost empty” I hear you asking.

Besides the wingsuit and the body of the pilot / rider, aerodynamic lift is also provided by the propellers. If they “look” slightly upwards, the component of the thrust force upwards completes the equation.

Thanks
Manolis Pattakos

[manolis]

Hello Tok-Tokkie.

I couldn’t describe better what we are trying to do. Thank you.

Thanks
Manolis Pattakos

[manolis]

Hello Uniflow.

You write:
“Nothing comes down faster than a vertical take off machine, upside down!”

Quote from http://www.para.co.za/Newsletter/TT20.htm :

So what sort of speeds are people getting to? So far only four people have gone faster than 500 km/hr. The current world record is 526.93 km/hr, set by Christian Labhart from Switzerland, and remember that is an average speed over the vertical kilometre. So he must have had a top speed of about 550 km/hr when he pulled out of the dive to slow down. That’s over two and half times the speed of flat flying. To get an idea of how fast that is, imagine standing on the edge of a sheer cliff and a 4-way FS team goes past at normal speed. That would look mind-bendingly fast. Now imagine being in a 4-way and a speed skydiver goes past. It would be even faster. Blink and you miss it. Now imagine being that speed skydiver.

You get out and pitch over smoothly into a head down position with your arms by your sides and your legs straight. The normal falling sensation that last a couple of seconds when you jump out just doesn’t go away. Not for the whole skydive. You never stop accelerating. The first time you try it, after about ten seconds you’ll think you’re going very fast, faster than you’ve ever gone before, and you’ll start getting scared. But you haven’t even started to get fast yet. At fifteen seconds you’ll think the airflow is about to rip your clothes off, and the sound of the air screaming past is louder than standing by the speakers at a Ramstein gig. At about twenty seconds you’ll enter the scoring zone. You’ll have probably given up all hope of surviving by now. The horizon is a blur, the airflow would make the Hiroshima blast seem like a butterfly flapping its wings, and permanent hearing damage will seem guaranteed. You will probably swear at this point. You steer by flexing your fingers and wiggling your toes, because it feels like doing anything else would result in a screaming, flailing, out of control, ball of limbs and ripped clothes. You’re in the scoring zone for about eight seconds if you going fast. That’s 8 seconds for 3300ft. And it just keeps getting faster and louder. You’re going twice as fast as Michael Schumacher has ever done, and you’re doing it without an engine. You know the planet is coming up fast. Very, very fast. At about twenty eight seconds you’re getting near the end of the scoring zone. You’ve given up all hope of getting away with this madness unscathed. And now you’ve got to try and slow down. You flare your nostrils just a bit and it pulls you out into a track that defies belief. People on the ground mistake you for a cruise missile heading for impact. The ground is still coming up alarmingly fast. After a second or so of tracking you’ll have crossed half of Africa and slowed enough to stick your arms and legs out. This is when you find that air at these speeds is not really a gas, it’s more like solid concrete. Your arms feel like you’re doing push ups with an elephant on your back, and you’ll think they are going to come out of their sockets. You slow down as much as you can, and pull when you have to. If you’re not all that good at slowing down, you’ve just got to take the hit. Brutal doesn’t describe it. Then you hang in the harness trying to get your breath back and come to terms with what you just did. It’s quite surreal hanging under a parachute in comparative silence and travelling slowly when you know you’ve just gone fast enough without an engine to do Jo'burg to Cape Town in two and a half hours.



Speed Skydiving - If you don’t see the Devil, you’re not going fast enough.

Tim Mace

End of Quote

Let’s make a rough calculation:

F = 75Kp = 750Nt (it is the weight if the falling SkyDiver)
Speed = 550Km/h = 153m/sec (it is the maximum falling speed )

Power = speed*force = 153m/sec * 750Nt = 115kW = 156PS

The Power is generated by the fall of the weight of the Skydiver and is consumed by the aerodynamic friction to maintain the top speed.


So, with the Portable Flyer on (i.e. with another, say, 100PS added to the above 156PS), the
maximum speed will rise from 550Km/h to some 700Km/h, however it is not a “free fall” any longer.

Dream / imagine going down with 700Km/h! Controllably

Thanks
Manolis Pattakos

[manolis]

Hello Gruntguru

Having the portable flyer secured on my shoulders / torso, I can move my shoulders a lot, changing the relative position / direction of body / rotors.

I think there is more control with the shoulders than with the hands holding some handlebars.

With the rider / pilot comprising the big part of the weight (we talk for less than 20Kg / 44lb total weight of the propulsion unit) the motion of the legs / hands of the pilot / rider seems more than adequate for the control.

On the other hand, extending the frame to form a pair of handlebars is easy and lightweight. So they can be made a pair of handlebars for “just in case”.

Practice will show whether they are necessary or not.


Here is a Jetpack similar to that of Rossy’s, with the difference that it can take-off the ground by its own, and it can land without a parachute:



It uses, just like Rossy’s JetPack, four Jet Engines.
The flight duration is similar to Rossy’s.

The pilot does hold handlebars:



Thanks
Manolis Pattakos

[manolis]

Hello all.

Technical Question:

With the two OPRE Tilting engines arranged the one over the other, and with each propulsion unit (comprising an OPRE Tilting engine and the two rotors it drives) being (by itself) completely neutral (its basis is perfectly rid of inertia vibrations and of combustion vibrations, its two rotors counter-rotate eliminating its total gyroscopic regidity, etc),

which is the preferable direction of rotation of the top rotors relative to the lower rotors?
And why?


Both arrangements work.

In the one arrangement (that shown in the animations), the two left rotors contra-rotate.

In the other arrangement:



the two left rotors rotate at same direction.


Is the preferable arrangement you see, the best for both: hovering and cruising?

Thanks
Manolis Pattakos

[tok-tokkie]

Kamov have contra-rotating rotors but that is so there is no reaction torque with their pair of stacked rotors.
In your case there is no reaction torque.
However twin blade turbo-prop engines use contra-rotating propellers because the rear prop can transfer more energy using that system. That is my understanding of it. Wiki points out that they tend to be noisy - but your rpm is much lower so that should not be an issue. https://en.wikipedia.org/wiki/Contra-ro ... propellers
The TU-95 is famous for its noise - amongst many other claims to fame.

[J.A.W.]

Splendid developments Manolis..

Certain matters will have to await actual test-flying though.. such as sound levels..

As for prop rotation, well, during WW2, certain twin-engined fighter planes ran 'handed' counter prop rotation..

Interestingly, both the P-82 Twin-Mustang & the DH Hornet had to swap the rotation sweep from
the original design setting - when flight tests showed up problems - that seemed counter-intuitive, but were real enough..

[autogyro]

Splendid developments Manolis..

Certain matters will have to await actual test-flying though.. such as sound levels..

As for prop rotation, well, during WW2, certain twin-engined fighter planes ran 'handed' counter prop rotation..

Interestingly, both the P-82 Twin-Mustang & the DH Hornet had to swap the rotation sweep from
the original design setting - when flight tests showed up problems - that seemed counter-intuitive, but were real enough..

The problems from the counter rotating 'air screws' on the twin Mustang and the DH Hornet was a result of the prop wash effect on airflow over the fuselage (twin booms Mustang).
Pee Wee Brown explained this to me in detail for the Hornet which he test flew and flew on operations.
The first attempts to sort this were on the Mosquito but this aircraft still remained a difficult one to take off and land with conventional rotation on its twin merlins.
Counter rotation resulted in high turbulence from the coneing effect that reduced control surface command at low speed and generated flutter at higher speeds.
I believe there were plans for both types to fit contra rotating units, somewhat cheaper than building rare left hand rotating Merlin engines.
The Shackleton I had the pleasure of flying had contra rotating air screws reduction geared from the crank shaft.
Some late spitfires and spitefuls had contra rotating Griffons but jets were coming in so few service machines developed this far.
The Manolis flyer has dual counter rotating air screws/rotors using pairs of rotors with separate power supplies.
I would love to see the airflow in a wind tunnel.
The air screw diameter is much smaller than the pusher propellers we used on our Wallis autogyros, they were around three feet depending on the blade number for engines used. Most we made by hand out of wood.
This small diameter was a problem for achieving maximum thrust.
The rpm had to be limited to 4,000 rpm to avoid tip speed problems full power extraction became very difficult even with multi blades.
I did intend to fit variable pitch when the more powerful engines we were working on were fitted but we never got that far.
90 hp was around the max we used, still got us all the world records.

I think Manolis has over compromised the aerodynamics in favour of the mechanical in this design.
I wont go into the control problems at this time.

[Andres125sx]

Manolis, thank you for sharing with us all your development, awesome job =D> =D> =D>

I hope you all your efforts are worth and you have great success!



What´s max thrust?

[manolis]

Hello J.A.W.

You write:
"Certain matters will have to await actual test-flying though.. such as sound levels."

I think it will be by far quieter than the JetPacks (based either on peroxide or on jet engines).


Quote from the Internet:

“On June 8, 1961, Harold Graham demonstrated Bell's "portable Army rocket" for the first time to an incredulous public. The flight saw Graham fly over a truck at a height of 15 feet landing 150 feet away after 14 seconds of air time. Nevertheless, the "ear-splitting" flight was described by the New York Times as "short but spectacular." By December 1961 Bell's 100-pound rocket belt would carry a man as high as 35 feet or a distance of 368 feet when barely skimming the ground.



By 1962, Moore's design was considered "perfected" with a top speed of 60mph, a top altitude of 60 feet, and 21 seconds of operation. Unfortunately, it also created 130 decibels of deafening noise — that's about as loud as a jet taking off from 200 feet away. Moore died in 1969 but variations of his original Rocket Belt design would be demonstrated around the world many years after his death. To this day, when you hear the word "jetpack," you're probably imagining Moore's Bell Rocket Belt design just before your sense of jilted entitlement sets in,”

End of Quote.

Thanks
Manolis Pattakos

[J.A.W.]

Sure Manolis, but your machine will have a designed flight time - 'orders of magnitude' - longer than a rocket..

T-T was concerned about the noisy contra-props featured by the big Russian Tu95 'Bear'..
..yet the props on those are so large - that the tips go supersonic, & that whip-crack noise is loud..

With your machine, you will have the sound of the props, & the exhaust of the engine too..

Have you got an exhaust pipe design - to show us?

Will it be a performance 2T - shaped chamber pipe with tail silencer..
..or perhaps simply an expedient use of the drive support shafts - such as outboard marine mills use?

[manolis]

Hello Andres125sx

"What´s max thrust?"

For high top speeds you need a lot of pitch.

On the other hand, with a big pitch (case of constant pitch rotors) the rotors require a lot of power from the engines at take-off and landing.

At take-off each propulsion unit alone (comprising an OPRE Tilting engine and the rotors it drives) has to provide a max thrust a little more than the total weight of the Portable Flyer (to allow the safe landing in case of malfunction of the other propulsion unit),

Thanks
Manolis Pattakos

[Tommy Cookers]

For high top speeds you need a lot of pitch.
On the other hand, with a big pitch (case of constant pitch rotors) the rotors require a lot of power from the engines at take-off and landing.
At take-off each propulsion unit alone (comprising an OPRE Tilting engine and the rotors it drives) has to provide a max thrust a little more than the total weight of the Portable Flyer

(in equivalent fixed wing aviation) propellors have composite-engineered structural properties giving some inherent pitch increase with flight speed ?
a big aspect of this rotor design ?

fwiw .....
to me it seems that the lower rotors would need more pitch than the upper, especially in the hover
and the pitch issue is more important than yesterday's issue (contra-rotation or not)

btw the Sea Hornet engines (130 series) got their handed rotation from differences in the reduction gearbox internals only
btw people should look at the A400M

[gruntguru]

Hello Gruntguru
Having the portable flyer secured on my shoulders / torso, I can move my shoulders a lot, changing the relative position / direction of body / rotors. I think there is more control with the shoulders than with the hands holding some handlebars.

Here is a Jetpack similar to that of Rossy’s, with the difference that it can take-off the ground by its own, and it can land without a parachute. It uses, just like Rossy’s JetPack, four Jet Engines. The flight duration is similar to Rossy’s.

The pilot does hold handlebars.

With the flyer strapped to your shoulders only, you will achieve neither the magnitude nor precision of thrust vectoring seen in that video.